The equine industry worldwide is continually improving breeding management. This improvement is driven by many factors; of significance are (i) the need to conserve "stallion power" and (ii) the veterinarians requirement to improve their efficiency by having mares ovulate with more predictability.
In order to achieve the above, the ability to predict, within predetermined time constraints when a mare will ovulate, is critical. The use of injection of human chorionic gonodotrophin (HCG) to stimulate ovulation in mares between 36-48 hours after application is widespread. However, despite success with this hormone, it has a number of serious drawbacks.
They include:
(i) it is not registered for this use in many countries (USA, and areas of Europe). Veterinarians using hCG in countries where it is unregistered are liable for any claims against failure of the product. PA1 (ii) continued used in the same mare can cause refractiveness--anaphylaxis is a possibility. PA1 (iii) hCG is derived from human urine either from pregnant or post menopausal women. Collection, isolation and purification are unpleasant, and the possibility of transmission of disease, particularly those of viral origin, is a risk. PA1 (iv) supplies of hCG cannot be guaranteed.
As an alternative to hCG, Leutinising Hormone Releasing Hormone (LHRH) has been injected into mares to stimulate ovulation. LHRH is also known as Gonodotrophin releasing hormone (GnRH). The LHRH stimulates the mare to produce its own gonodotrophin which, in turn, stimulates ovulation. An agonist of LHRH (Buserelin) has also been injected into mares and it has been reported that ovulation may be induced by such injections. Injected hormones must be typically administered a number of times to be successful and they are required in relatively large doses.